Both young and old enjoy forming shadow images. Usually a dark room is used, with a light being arranged so that a subject located between the light source and a wall surface casts a shadow on the wall. It is fun to trace the outline of the shadow on a piece of paper applied to the wall surface, and thereby provide a permanent image of persons and things.
While this is an entertaining and fascinating pastime, it would be desirable to be able to more rapidly place one's image on a sheet of material attached to the wall, and to be able to instantaneously erase the image. It would also be desirable to be able to utilize such a pastime in conjunction with permanent indicia previously placed on the sheet of material. Apparatus and method which achieves this desirable goal is the subject of the present invention.
Luminescence is the emission of light by various materials, such as glowworms and luminous paints. The term "fluorescence" is sometime accepted as an analogous word. Hence, the term "luminescence" has been accepted for all light phenomena other than incandescence, and it includes a phosphor, an ingredient that emits light for a certain length of time after exposure to an outside energy source. Sufides, including calcium sulfides, are such phosphors. Certain metal oxides, silicates, phosphates, and the sulfides of zinc and cadmium will luminesce if prepared by special procedure.
As used herein, the term "luminous powder" or "luminous material" is intended to include any non-toxic material that glows in the dark after having been subjected to a source of light, so long as the luminous material is compatible with the present invention.